Jerry Jensen's ATM idea

[Jerry]

http://einstein.stanford.edu/highlights/hl.html

Now that the gyro polhode behavior is well understood, we have been able to shift our focus to identifying and addressing some subtle systematic sources of noise and interference that are buried in the data, along with the relativity signals. Identifying and removing as many of these subtle systematic effects as possible is critically important for reducing the margin of error in our final results—especially the frame-dragging result. While we have been making steady progress in these efforts, it has proven to be a slow and painstaking process, and it is now apparent that several more months of data analysis will be required to achieve the lowest possible margin of error.

When this probe was launched, the PIs were confident that the results would be fairly easy to extract, in fact the algorythms which were to be used in the analysis were already written - this is really necessary if the resulting science is to provide objective evidence of GR. Constantly processing data that did not live up to expectations until victory can be claimed is questionable science.

we ask NASA to create a contingency plan, and budget for an extension of the data analysis phase for several months past our scheduled results announcement at the American Physical Society (APS) meeting on 14-17 April 2007 in Jacksonville, FL. To this end, following a meeting with NASA in mid January, NASA has requested a proposal for extending the GP-B data analysis phase through December 2007, and this is in progress.

This makes the Gravity B probe data analysis just as suspect, and almost as late as WMAP.

In late fall, 2007, playing the role of our own harshest critic, our science team will perform a careful and thorough final review of the analysis and results, checking and cross-checking each aspect to ensure the soundness of our procedures and the validity of our outcomes.

No. I am. You have failed to meet your own criteria for success: You failed to characterize the properties of the Gravity B probe gyroscopes before the mission well enough that they did not have to be recalibrated in-flight.

There has been considerable technical merit in this quest - a great science project, and I will be interesting in reading about the proper motion of the quasars involved in the calibration process (after the PI embargo is lifted), but as a validating test of GR, this effort is a failure - Just like Pioneer 6.

[Jerry]

I didn't bother to post a prediction for Rosetta; in part because I had so little information - I did not know if this was a 'braking' or 'accelerating' gravity assist, and in any case, I did not expect the ESA to release any numbers.

But I did not count on Doug Ellison having access to the control room while writing a column for the Planetary Society webblog:


[Quote=Ellison]He gave us the bare stats of the flyby: closest approach at 01:57:59 at a height of 249.1 kilometres with a three-sigma (i.e. how accurate that figure is) of 3 kilometres.

And later, in the same blog:

For now, the important fact is that the spacecraft performed perfectly: the trajectory was about a dozen kilometres off the target point. which they are more than happy with.

Since orbital trajectories are a little like a game of horseshoes, 12km is a ringer; but why was it off-target by four times the predicted three sigma? That is ~6 sigma, and that is a long way off for a probe under Newtonian control:

The last trajectory correction manoeuvre was on February, the 9th, with a change of just 4.55 centimeters per second, which moved the spacecraft's aim point at Mars by about 60 kilometres.

So they made a trajectory correction two weeks ago, then missed their quoted three sigma by 400%! That is worse than the ~350% error in the models predicting MRO aerobraking over the poles.

At 250 km, it is difficult to blame the fickle atmosphere of Mars. He doesn't say whether it was 12 km closer or further from Mars than expected, but I will bet next weeks winning lottery ticket that Rosetta passed 12 km closer-than-expected!

Which also brings us back to the Mars Climate orbiter: In spite of the nefarious metric-english unit error, the probe was still predicted to be ~100 km at closest approach. A 12 km error like Rosetta's would have pushed the Climate orbiter inside the drop-dead 90 km limit. Both Spirit and Opportunity overshot the ideal target by 8-12 km - inside 3 sigma, but the three sigma was based in part on the earlier landers, which were also 'downwind'.

(A minor bit of physics here: If Mars is slightly heavier than orbital predictions, the atmosphere is also thinner at high altitude and thicker near the surface. Since the velocity component tangent to the planet is much greater at higher altitude than near the surface, if the planet is 'heavy', the trajectories should all be longer-than-expected.)

Are we navigating this poorly, or is gravity behaving somewhat badly?

[Jerry]

There is a good Raph Lorenz presentation on the sands of Titan here:

http://saturn.jpl.nasa.gov/multimedi...ARM_Lorenz.pdf

The quest continues for an organic substance that has the physical properties of silicate sand: The same range of colors, refractive index, emissivity, friability, permiability, bulk packing, and dune forming capability.

Carl Sagan started looking for the 'right stuff' three decades ago, predicting the atmosphere would condense into 'tholins', a word not found in the volcabulary of chemists. Other reseachers are calling the sands of Titan 'smirt' or 'smust' composed of hard spherical organic balls.

This is not totally impossible - nanotubes, buckyballs, crystalized carbon have some of these attributes. Unfortunately the temperatures needed to produce carbon compounds in these forms are high, and the compounds tend to be black - lots of different wavelengths of absorption bands.

It is fortunate that Newtonian gravity does not allow the surface of Titan to be constructed out of the same materials as Mars, the moon, or the Earth. Because some time, hopefully in this century, we will return to Saturn with a better tool for looking at the composition of the planets and the moons. The correct conclusion will be unavoidable...in less than a century. (I hope - I thought the Cassini Huygens mission would put the issue to rest, but the observational evidence is having a tough time dispelling a three hundred year old theory.)

We know how organics behave - they form oils, waxes, and under a lot of pressure, coal. Simple carbon bonds do not have the strength to turn carbon into sand.

[nutant gene 71]

http://einstein.stanford.edu/highlights/hl.html


When this probe was launched, the PIs were confident that the results would be fairly easy to extract, in fact the algorythms which were to be used in the analysis were already written - this is really necessary if the resulting science is to provide objective evidence of GR. Constantly processing data that did not live up to expectations until victory can be claimed is questionable science.


This makes the Gravity B probe data analysis just as suspect, and almost as late as WMAP.

..snip..

It looks like the next real announcement on the data from GP-B will be in April's APS meeting, though may not make the popular press until year end, so we may not know final results until fall 2007. Finessing error of margins is the right way, though I hope they are as critical of their own methodology in doing so as of the data noise removal. As they say:

In late fall, 2007, playing the role of our own harshest critic, our science team will perform a careful and thorough final review of the analysis and results, checking and cross-checking each aspect to ensure the soundness of our procedures and the validity of our outcomes. We will then convene a final SAC meeting to obtain the committee's independent review of the final results. Moreover, we will seek independent reviews from a number of international experts.

Rigorous science should lead to good results. Will they find what they hope to find, I wonder? We'll see if GR is what it states to be, or perhaps something else.